WO2003040757A2 - Procede et dispositif permettant d'empecher l'accumulation des signaux - Google Patents

Procede et dispositif permettant d'empecher l'accumulation des signaux Download PDF

Info

Publication number
WO2003040757A2
WO2003040757A2 PCT/US2002/032788 US0232788W WO03040757A2 WO 2003040757 A2 WO2003040757 A2 WO 2003040757A2 US 0232788 W US0232788 W US 0232788W WO 03040757 A2 WO03040757 A2 WO 03040757A2
Authority
WO
WIPO (PCT)
Prior art keywords
signal
energy
weighted
signals
pile
Prior art date
Application number
PCT/US2002/032788
Other languages
English (en)
Other versions
WO2003040757A3 (fr
Inventor
Wai-Hoi Wong
Hougdi Li
Jorge Uribe
Hossain Baghaei
Original Assignee
Board Of Regents, The University Of Texas System
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Board Of Regents, The University Of Texas System filed Critical Board Of Regents, The University Of Texas System
Priority to EP02799158A priority Critical patent/EP1444534A2/fr
Priority to CA002463756A priority patent/CA2463756A1/fr
Publication of WO2003040757A2 publication Critical patent/WO2003040757A2/fr
Publication of WO2003040757A3 publication Critical patent/WO2003040757A3/fr

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/161—Applications in the field of nuclear medicine, e.g. in vivo counting
    • G01T1/164—Scintigraphy
    • G01T1/1641—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras
    • G01T1/1642—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras using a scintillation crystal and position sensing photodetector arrays, e.g. ANGER cameras
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/42—Arrangements for detecting radiation specially adapted for radiation diagnosis
    • A61B6/4208—Arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a particular type of detector
    • A61B6/4258—Arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a particular type of detector for detecting non x-ray radiation, e.g. gamma radiation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/17—Circuit arrangements not adapted to a particular type of detector
    • G01T1/171—Compensation of dead-time counting losses
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
    • A61B6/03—Computed tomography [CT]
    • A61B6/037—Emission tomography

Definitions

  • RO1-CA61880, NIH-RO1-CA58980, IH-RO1-CA76246, and N1H-RO1-CA58980S1 from the National Institutes of Health — National Cancer Institute.
  • the present invention relates generally to the field of radiation detection and imaging technology, hi particular, the present invention maybe used for processing exponentially decaying pulses from a scintillation detector or a similar detector for radiation particles.
  • a radiation particle gamma ray, neutron, electron, etc.
  • the scintillation detector will emit light, which is then converted into an electronic signal by a photosensor (e.g., photomultiplier tube or photodiode).
  • a photosensor e.g., photomultiplier tube or photodiode.
  • This electronic signal can then be received and processed by electronic circuits.
  • the scintillation light decays exponentially with a time constant ⁇ (the time when the light level decays to 37% of the onset level), as shown in FIG. 1.
  • FIG. 1 shows energy output by two gamma ray particles over time. Since the total amount of light emitted by the scintillation detector represents linearly the energy deposited by the radiation particle in the detector, the area or integral under the curves in FIG. 1 is a measure of the particle energy. As shown in FIG. 1, area 5 and area 10 define a measure of the particle energy of the gamma ray particles. Furthermore, the initial peak in the light level is also proportional to the radiation energy. Hence both the area 5 and peak VI in FIG. 1 may be used to measure the energy of the gamma ray or radiation particle.
  • the integral (the total amount of light emitted) is generally used to measure the radiation energy.
  • the radiation flux increases, it becomes increasingly likely that the next radiation particle may arrive at the detector while all previous events are still emitting light (FIG. 2).
  • the identity of each individual radiation particle will be lost, and several particles will merge into one large signal, as shown in FIG. 2.
  • neither the peak level (VI or V2 of FIG. 1), nor the integral information (area 5 or area 10 of FIG. 1) can be used to separate or measure the energy of each particle. In these situations, the detection system will fail to respond properly because of erroneous measurement.
  • the time-lapse between two events is a random distribution (i.e., the time-lapse between two events is a random variable) centered about the "average arrival time"
  • the probability that two events will come closer than Ax would be approximately 10% (using Poisson statistics).
  • the head-room factor as a function of pile-up percentage is shown in Table 1 below:
  • a lOx head-room is a reasonable choice, and is generally practiced in the prior art.
  • a prior art detector When coupled with a Ax light-collection time (system dead-time), such a prior art detector provides a measured-energy error (due to pile-up) of less than approximately 2% for approximately 90% of the time, and an energy measurement error (energy resolution) greater than 2% for approximately 10% of the time.
  • This minimum lOx head-room (40 ⁇ ) timing requirement means that the maximum detection-rate should be less than l/(40 ⁇ ) for the scintillation detector.
  • the present disclosure permits a scintillation detector system to operate at a much higher event-rate (count-rate) by obviating the lOx head-room factor without pile-up.
  • the techniques of this disclosure maintain a greater event-rate with little sacrifice in the total amount of scintillation light collected, specifically at a 10 times higher radiation flux with little or no sacrifice in measurement accuracy. If the fraction of scintillation light collected can be reduced (i.e., if a user is willing to compromise measurement accuracy), the present disclosure allows detectors to count at count-rates approximately twenty times greater than conventional methods. Techniques of the present invention may be termed HYPER (High-Yield-Pileup-Event- Recovery).
  • This disclosure proposes different implementations to execute HYPER mathematics to either improve resolution of the total energy (or position) estimation for the HYPER method or to provide a simple way (or a faster way) to further increase count-rate using a multiple HYPER zone method. This disclosure also shows how to use a HYPER circuit in the application of coincidence imaging.
  • the present invention includes an apparatus for signal pile-up prevention, comprising a delay circuit for receiving, holding, and passing an incoming signal; a computation circuit for determining a weighted value of the incoming signal; a sampling circuit for receiving the weighted value.
  • the sampling circuit passes the weighted value (which may be passed to an A/D converter) upon receipt of a triggering signal, which corresponds to receipt of a next incoming signal at a trigger circuit.
  • the computation circuit may comprise an amplifier, an integrator, and an adder.
  • the weighted value is a sum of an integrated value and an instantaneous value, and may be a substantially constant value.
  • An apparatus may also include a smoothing circuit connected to the circuit adapted to receive the incoming signal.
  • the apparatus may also comprise a residual subtraction circuit for reducing the weighted value by a residual signal value.
  • the sampling circuit discharges said weighted value upon input of the triggering signal.
  • the present invention may be used in connection with nuclear medicine applications, such as a PET or gamma camera, and may be used to determine both energy and position information.
  • a nuclear medicine application such as a PET or gamma camera
  • Such an apparatus comprises a plurality of delay circuits, a plurality of computation circuits, and a plurality of sampling circuits, wherein each of the delay circuits receives a different incoming signal from a different output of a gamma camera.
  • the delay circuit, computation circuit, and sampling circuit comprise a pile-up prevention circuit.
  • Particular embodiments will comprise a plurality of pile-up prevention circuits, and may include a digital signal processor and fast trigger connected to each of the pile-up prevention circuits. Such an embodiment may also comprise an inter-zone detection circuit connected to the fast trigger and a multi-zone-trigger processor connected to said inter-zone detection circuit, capable of centroid averaging.
  • An exemplary embodiment may have a plurality of fast triggers.
  • a method for preventing signal pile-up may comprise: delaying an incoming signal for a preselected time prior to passing the incoming signal; computing a weighted value of the incoming signal; and sampling the weighted value upon receipt of a triggering signal from the next radiation particle, thereby preventing signal pile-up.
  • Computing may include amplifying the incoming signal to obtain an amplified signal, integrating the incoming signal to obtain an integrated signal, and adding the amplified signal and integrated signal to obtain the weighted value. This method thereby creates a variable signal collection time.
  • Another method may determine position and energy information of incoming signals without pile-up.
  • Such a method may include: delaying at least one prenormalized position signal and a total energy signal; computing a weighted value for each prenormalized position signal and the total energy signal; sampling the weighted value for each prenormalized position signal and the total energy signal, upon receipt of a triggering signal from the next radiation particle.
  • the prenormalized signals and the total energy signal may be corrected by subtracting remnant values of all previous signals.
  • the present invention comprises an apparatus for dynamically detecting energy of each one of a plurality of incoming signals received from a detector, without pile-up of previous incoming signals, including: a delay circuit connected to receive an incoming signal from the detector and to pass the incoming signal from an input to an output of the delay circuit after a time delay; a trigger circuit connected to receive the incoming signal from said detector, and for generating a triggering signal upon receipt of a subsequent incoming signals at the trigger circuit; a computation circuit connected to the output of said delay circuit for determining a weighted value of the incoming signal; a sampling circuit connected to receive the weighted value from said computation circuit, and for passing the weighted value from an input to an output of the sampling circuit upon receipt of the triggering signal; and a residual subtraction circuit connected to the output of said sampling circuit, for subtracting a residual signal value corresponding to a residual weighted value of previous incoming signals, and for providing an output signal corresponding to the energy of the incoming signal.
  • Another aspect of the present invention comprises an apparatus connected to a gamma camera for detecting position and energy information of each one of a plurality of incoming signals received by the gamma camera, without pile-up of previous incoming signals, including: a first delay circuit connected to receive a first incoming signal from the gamma camera, and for passing the first incoming signal from an input to an output of the first delay circuit after a first time delay; second and third delay circuit arranged like the first delay circuit to receive, delay, and pass, second and third signals; a trigger circuit connected to receive the third incoming signal from said gamma camera, and for generating a triggering signal and a timing mark upon receipt of a next third incoming signal at the trigger circuit; first, second and third computation circuits, each connected to receive an output of a respective one of the first, second, and third delay circuits, and for determining a respective weighted value for each of the first, second, and third incoming signals; first, second and third sampling circuits, each connected to receive a respective one
  • Another aspect of the present invention resides in a method of obtaining energy information for each one of a plurality of incoming signals received from a detector, without signal pile-up, comprising the steps of: delaying an incoming signal for a preselected time; computing a weighted value of the signal after the preselected time; sampling the weighted value upon receipt of a subsequent signal; and subtracting a residual signal value from the weighted value to obtain the energy information.
  • the residual signal value may correspond to a residual weighted value of at least one previous incoming signal, thereby preventing signal pile-up.
  • Yet another aspect of the present invention resides in a method of determining position and energy information of a plurality of incoming signals from a detector without pile-up, comprising the steps of: receiving a first and second prenormalized position signal and a total energy signal from the detector; delaying the first and second prenormalized position signals and total energy signal for a preselected time; computing a weighted value for each of the first and second prenormalized position signals and total energy signal after the preselected time; and sampling the weighted value for each of the first and second prenormalized position signals and total energy signal upon receipt of a subsequent first and second prenormalized position signals and total energy signal.
  • the methods of the present invention maybe used to operate gamma-cameras (or other radiation detectors) in very high count-rate situations.
  • the present invention includes the following features: (a) no compromise in measured energy-resolution in low count rates; (b) count recoveries and accurate energy measurement even for gamma-rays within a pile-up involving multiple gamma-rays; (c) optimal scintillation-light collection in very high count-rate situations; and (d) ability to merge with a multi-zone architecture to further increase count-rate capability.
  • the present invention includes algorithms that apply to all triggering gamma-rays (it is to be understood that although gamma-rays are discussed herein, the present invention applies to all types of radiation detectors), for extracting the correct energy and position of every triggering gamma-ray.
  • This disclosure also provides ways to improve energy and position resolution for the HYPER (High-Yield-Pileup-Event-Recovery) method and illustrates how to use that method in the application of coincidence imaging.
  • Conventional single-scintillation-crystal design coupled with conventional detector electronics and the traditional Anger-position algorithm may all hinder higher count-rate imaging because of the pileup of gamma ray signals in the detector and electronics.
  • the fraction of nonpileup events is ⁇ 20% of the total incident events.
  • the recovery of pileup events may significantly increase the count-rate capability, increase the yield of imaging photons, and minimize image artifacts associated with pileups.
  • HYPER solves the pileup problem.
  • One main idea of HYPER may be stated as (a) dynamic integrating: if no pileup happened, a signal from an event maybe integrated for a fixed time (e.g., 3 to 4 times the scintillation decay time) to fully collect all the light (signal) to maximize detection accuracy (resolution); however, if a pileup is detected, the integration of the current signal stops immediately; (b) calculating a weighted value: a weighted value is the estimated total energy that includes the energy of the current event and a residual energy from all the previous events; (c) remnant correction: calculating a pile-up free energy from two consecutive weighted values.
  • FIG. 20 shows an exemplary diagram of one embodiment of HYPER techniques.
  • the energy and pre-normalized position signals from a gamma camera are delayed for a fixed period of time.
  • the energy-signal pulse goes to a triggering circuit that generates a trigger and a timing mark at the leading edge of the event-signal.
  • the computation circuit generates a weighted value estimating a total energy or pre-normalized position signal that includes the contribution from the current event and the remnant signals from all the previous events.
  • the present-event weighted value is sampled and buffered, and two consecutive weighted values are used for the correction of residual signals from all previous events.
  • HYPER methodology may be implemented and improved upon in several ways. Different implementations may use the same procedure and mathematical formulae as the basic HYPER method mentioned above in (a), (b) and (c). Different implementations have different advantages and trade-offs in signal noise and processing speed. When the signal noise is high, a lower noise weighted value for estimating the total energy may be extracted in several different ways:
  • weighted-sum is the total energy in theory, but it can be noisy because the instantaneous value itself has more noise than the integrated value.
  • the weighted-sum signal may go through an analog low-pass filter, and the filtered weighted-sum may be continuously or multiply sampled. Then, a digital filter such as median filter or a decay filter may be applied to those samples to generated a low noise weighted value.
  • the integrated value may be dynamically weighted by a factor.
  • FIG. 25 shows a large detector divided into four zones (zones K, L, M and N). Since every two neighbor zones share one row or one column of photomultiplier tubes (PMT), one gamma hit may trigger two zones if its energy is collected by the shared PMTs. To find out the zone that has the "real" hit, a threshold may be set for the pre-normalized position signals of each zone to reject the "false" hit from its neighbor zone.
  • PMT photomultiplier tubes
  • FIG. 26 shows an example of a two-zone design. Each zone has one independent block detector coupled to 4 PMTs.
  • the HYPER method combined with multiple zones may significantly increase the count- rate capability and dose efficiency of gamma cameras.
  • coincidence detection applications such as, but not limited to, positron coincidence imaging
  • a special additional technique is provided in this disclosure.
  • integration time is fixed; therefore, the end of integration and signal-digitization (for energy and position) is synchronized with the trigger signal (just delayed by the fixed integration time).
  • the trigger signal is generated at the leading edge or the arrival time of the event.
  • Coincidence detection can be performed between the ends of signal digitization or the trigger signals.
  • HYPER uses a dynamic integrating method, which means the measured energy and position signals are no longer synchronized with the leading-edge of the present triggering signal because the energy and position signals are only generated or digitized at the arrival of the next event (arriving at a random time from present event).
  • a trigger signal may be delayed by a fixed time and a new synchronization may be setup between the delayed trigger and the energy/position signals before they can go to a coincidence procedure.
  • the energy and position signals of all events may be buffered into a FIFO (first-in-first-out) queue.
  • a delayed trigger signal may be used to read them out individually to restore the synchronization between the events output of the FIFO. This process is shown generally in FIG. 27.
  • the fixed delay time should be longer than the maximum integrating time.
  • the trigger delay circuit should have good timing-resolution and a small dead time.
  • the HYPER methodology of this disclosure, the multiple HYPER zones method, and the event-synchronization method for coincidence detection may all improve PET camera imaging performance and facilitate gamma cameras for radionuclide therapy dosimetry imaging, cardiac first-pass imaging, positron coincidence imaging, and the simultaneous acquisition of transmission and emission data using difference isotopes with less-contamination between transmission and emission data.
  • Those having skill in the art, with the benefit of this disclosure, will recognize additional suitable uses for these techniques.
  • FIG. 1 is a graphical representation of scintillator light output of gamma rays over time.
  • FIG. 2 is a graphical representation of scintillator light output of a plurality of radiation particles having pile-up.
  • FIG. 3A is a graphical representation of exponential decay of a radiation particle over time.
  • FIG. 3B is a graphical representation of total integrated energy from a radiation particle.
  • FIG. 4A is a graphical representation of a weighted instantaneous and integrated signal of a radiation particle according to the present invention.
  • FIG. 4B is a graphical representation of a weighted sum of an instantaneous signal and an integrated signal of a radiation particle according to the present invention.
  • FIG. 5 A is a block diagram of an exemplary embodiment of the present invention.
  • FIG. 5B is a block diagram of another exemplary embodiment of the present invention.
  • FIG. 6 is a block diagram of an exemplary apparatus according to the present invention.
  • FIG. 7 is an illustration of a PMT configuration that may be used in accordance with the present invention.
  • FIG. 8 is a representation of boundary artifact generation.
  • FIG. 9 is a block diagram of an exemplary apparatus according to the present invention.
  • FIG. 10 is an illustration of study results according to the present invention.
  • FIG. 11 is a graphical representation of scintillator light output of a plurality of radiation particles having continuous pile-ups.
  • FIGS. 12A-12B are graphical comparisons of energy spectra of count-rates of prior art methods (FIG. 12A) and methods according to the present invention (FIG. 12B).
  • FIGS. 13A-D are graphical representations of energy spectrum of an apparatus according to the present invention at very high count-rates.
  • FIG. 14 is a graphical representation of energy resolution (percentage error) as a function of count-rates of prior art methods and methods according to the present invention.
  • FIG. 15 is a graphical representation of detected count-rates as a function of true count- rates of prior art methods and methods according to the present invention.
  • FIG. 16 is a graphical representation of energy spectrum of a delay line pulse clipping method.
  • FIGS. 17A-F are graphical representations of energy spectrum of a 99m Tc source with and without remnant subtraction.
  • FIG. 18A is a representation of a Monte Carlo result according to the present invention.
  • FIG. 18B is a representation of a Monte Carlo result of a pulse clipping method.
  • FIG. 18C is a representation of a Monte Carlo result of a conventional fixed integration method.
  • FIG. 19 A is a flow chart of an exemplary method according to the present invention.
  • FIG. 19B is a flow chart of another exemplary method according to the present invention.
  • FIG. 20 illustrates an exemplary circuit according to one embodiment of the present disclosure.
  • FIG.21 illustrates a pileup condition according to one embodiment of the present disclosure.
  • FIGS. 22-24 illustrate various calculation circuits according to embodiments of the present disclosure.
  • FIG. 25 illustrates a four-zone detector according to an embodiment of the present disclosure.
  • FIG. 26 illustrates zone identification techniques according to an embodiment of the present disclosure.
  • FIG. 27 illustrates a coincidence calculation circuit according to an embodiment of the present disclosure.
  • FIG. 28 illustrates a high resolution time lapse measurement circuit according to an embodiment of the present disclosure.
  • the present invention in a broad aspect comprises a dynamic pile-up prevention technique for increasing the count-rate capability of scintillation detectors.
  • a NaI(Tl) scintillator may be used to illustrate the method.
  • NaI(Tl) scintillators are discussed herein, the present invention is applicable to other detectors, such as BGO, GSO, LSO, plastic, and Csl.
  • the dynamic pile-up technique of the present invention has a variable detector signal collection time (deadtime), whereas conventional systems typically have a fixed deadtime of 1 ⁇ s (4 ⁇ ) for Nal(Tl) scintillators.
  • Position sensitive detectors with Anger decoding algorithms are used in SPECT cameras and PET cameras (Nal(Tl), BGO and LSO systems) to reduce production costs.
  • One drawback of Anger detectors is lower detection rates because all the photomultipliers (PMT's) involved in the localization of an incident event will be engaged in signal collection for a fixed time period, thereby inhibiting the detection system to process a second event incident within this time period. From energy and spatial resolution considerations, a fixed signal-collection time period of 2 ⁇ s to 3 ⁇ s is preferred, where ⁇ s is the scintillation decay-time constant.
  • the average time lapse between two events should be 10 times the signal collection time (20 ⁇ s - 30 ⁇ s ) to reduce the probability of signal pile-up to 10%.
  • this limiting average time lapse would be 5-9 ⁇ s, which corresponds to a maximum count rate of 110-200 thousand-counts/sec (Kcps) per crystal or crystal-block, which has been the maximum count-rates of most gamma-cameras and BGO block detectors for many years.
  • Kcps thousand-counts/sec
  • DLPC delay-line pulse-clipping
  • the weighted sum is generally not equal to the energy of an impinging event (See Appendix), because it also includes the remnant light from all previous events.
  • the weighted sum is only equal to the event energy when the first event in the two-event pile-up is not a pile-up on previous events, which is a condition in contradiction with very high count-rate situations, where most events are riding on the signal of one or more previous events.
  • the errors in this energy measurement method will be large in very high count-rate situations (when many events are part of multiple-event pile-ups), as shown in the following table derived from Poisson's statistics for Nal(Tl) for the probabilities of multiple-event pile-ups within 1 ⁇ s:
  • the present invention provides a new approach for preventing signal pile-up, namely, a hybrid signal processing method based on several concepts. It is known that after a scintillation crystal detects a gamma ray, the light output decays exponentially. This signal is illustrated in FIG. 3 A, together with its one-standard-deviation ( ⁇ ) error boundaries. Initially, about 40 electrons per 10 ns period are generated from a 140 KeN energy deposition (from 99m Tc). The total integrated signal over a period of 1 ⁇ s is approximately 1000 electrons from this 140 KeN energy deposition event, as shown in FIG. 3B.
  • the initial signal would be 20 electrons per 10 ns period, and the total integrated signal would be 500 electrons.
  • these numbers are specific for gamma rays detected by a ⁇ a ⁇ (Tl) scintillation detector, the same general principles, and the general curves shown in
  • FIGS. 3 A and 3B apply to other radiation particles and other radiation detectors.
  • both the instantaneous signal and the integrated signal may be used to determine the detected gamma energy.
  • the percentage-error is much less with the integrated signal collected over 1 ⁇ s, as shown in FIG. 3B. For this reason, only the integrated signal technique is used traditionally.
  • the present invention includes a hybrid signal processing technique that uses both the instantaneous signal and the integrated signal together to help derive the radiation energy, since both signals contain radiation energy information.
  • the instantaneous scintillation signal from the photomultiplier-tube (PMT) may be smoothed with a filter, for example a 10 ns time-averaging RC-filter.
  • a filter for example a 10 ns time-averaging RC-filter.
  • the smoothed instantaneous signal and the integrated signal are shown in FIGS. 3 A and 3B.
  • the smoothed instantaneous signal is amplified to the equivalent of 1000 electrons at time zero, and this amplified instantaneous signal is summed with the integrated signal (unamplified) as shown in FIG. 4A.
  • the smoothed instantaneous signal may be amplified to various levels, depending upon the type of radiation and detector. In certain embodiments, the smoothed instantaneous signal need not even be amplified.
  • the resultant weighted-sum signal of the instantaneous signal and the integrated signal is a constant and is always a measure of the radiation energy if the event is not a pile-up on previous events, regardless of when the sum-signal is sampled.
  • the sampled signal amplitude may always be 1000 electrons, which is equivalent to a 140 KeN energy deposit.
  • the sum signal acquired in the duration of the present event is sampled. If a next gamma ray arrives within 1 ⁇ s, the signal (sum) in the duration of the present gamma ray is sampled immediately before the scintillation signal of the next gamma ray reaches the signal measurement circuit.
  • the measured signal sum relating to the present gamma ray excludes the erroneous pile-up signal from the next gamma ray.
  • the signal sum may still contain signals from previous events.
  • FIG. 19 A A flow chart of an algorithm according to the present invention is shown at FIG. 19 A.
  • a detected signal is integrated in step 210, is amplified in step 220, and causes a trigger signal in step 230.
  • the integrated value of the detected signal and the amplified value of the detected signal are summed in step 240.
  • the summed value is stored in step 250 and is sent also to the residual subtraction circuit for use in processing.
  • the trigger signal from step 230 is sent to determine time lapse between the present detected signal and the previous detected signal in step 260.
  • the sum of the previous detected signal is multiplied by an exponential of the time lapse in step 280. This value is then subtracted from the present detected signal sum value in step 270.
  • the output of step 270 is the detected energy signal Ej, as shown in step 290.
  • FIG. 5 A A block diagram of an exemplary embodiment of the present invention that implements this technique is shown in FIG. 5 A.
  • the exemplary pile-up prevention circuit 100 receives electrical signals from a photosensor (not shown in FIG. 5 A) connected to the input of the circuit.
  • the pile-up prevention circuit (PPC) 100 includes a timing trigger 110, which provides a signal to the sample and discharge control circuit 170 and residual subtraction circuit 190 upon receipt of a signal.
  • the timing trigger 110 may be a simple threshold discriminator or a delay-line clipping discriminator, which minimizes retriggering by the remnant signal of the same particle.
  • the timing trigger 110 may be another appropriate triggering device, for example, a Schmitt trigger.
  • PPC 100 also includes a smoothing circuit 120 to smooth the received signal.
  • the smoothing circuit 120 may be a filter, such as a low-pass RC filter or a slow amplifier. Further, in certain embodiments, a smoothing circuit may not be necessary.
  • the smoothed signal passes to a delay circuit 130, which provides a desired delay to the signal before application to the calculation portion of the circuit.
  • the delay circuit 130 may be a delay cable or analog delay line integrated circuit. The delay circuit 130 may provide for a delay of between about 1 to 100 ns, and more preferably between about 5 to 50 ns.
  • the calculation portion of PPC 100 includes amplifier 140, integrator 150, and adder 160.
  • the amplifier 140 amplifies the smoothed signal, thereby providing a weighting factor to the signal. As discussed above, in an exemplary embodiment the amplifier 140 amplifies the signal to 1000 electrons. In appropriate embodiments, an amplifier may not be necessary.
  • the integrator 150 performs an integration of the signal over the exponential decay of the signal. The outputs of the amplifier 140 and integrator 150 are input into the adder circuit 160, which develops the sum of these signals. The resultant sum is forwarded to sample and discharge control circuit 170.
  • the sample and discharge control circuit 170 maybe comprised of a register or the like, and a control circuit, such as a fast analog switch, FET transistor, or the like.
  • the sample and discharge control circuit 170 passes the resultant sum to analog to digital converter (ADC) 180.
  • ADC analog to digital converter
  • the ADC 180 converts the sum to a digital signal, which is then forwarded as the weighted-sum signal to the residual subtraction circuit 190, which subtracts any remnant signal from previous radiation events.
  • the residual subtraction circuit 190 includes a lapse timer 192, which determines a ⁇ T (or time difference) corresponding to the time between receipt of two detected signals.
  • the residual subtraction circuit 190 also includes a look-up table 194 that determines an exponential value based on the time difference. This exponential value is then multiplied by the previous sum signal Si-i (not shown).
  • a subtractor 196 subtracts this remnant sum signal from the sum signal S; relating to the present detected signal to thereby output a digital signal E, corresponding to energy value of the present signal.
  • the sample and discharge control circuit 170 discharges the output of the integrator 150 to zero immediately by sending a control signal upon receipt of the signal from the timing trigger 110 to a capacitor and switch (not shown) associated with the integrator 150.
  • the timing trigger 110 senses the arrival of the initial burst of scintillation, electrons from any gamma ray. Immediately, time trigger 110 sends a signal to the sample-and-discharge control circuit 170 to sample the weighted sum of the previous gamma ray and pass the sum signal to the ADC 180. Since the timing trigger 110 has no delay, whereas the sum signal processing branch is delayed (in an exemplary embodiment, the delay may be between about 1 and 100 ns, and more preferably be between about 5 and 50 ns) with a delay circuit 130, the weighted-sum signal is sampled before the arrival of the energy signal from the next gamma ray. The delay is used to ascertain that the weighted sum of the present event is sufficiently discharged before the next event enters the integrator 150.
  • the delay also provides enough time delay for the sample-and-discharge control circuit 170 to discharge (to zero) the previous integrated signal from the integrator 150 before the arrival of the next signal, which prepares the integrator 150 for the next signal. The discharge avoids pile-up of the old integrated signal onto the new integrated signal.
  • a dual-integrator design (“ping-pong") may be used as the integrator, with each integrator 150 A and 150B taking turns in processing each consecutive event as follows: when a present event is detected, the circuitry will be switched via switch 145 to integrator 150A to integrate the signal of the present event; when the next event is detected, integrator 150A will stop integrating the present event and the integrator output will be sampled.
  • integrator 150A is discharged in this idle duty cycle when the integration of the next event is performed by integrator 150B. This will provide more than enough time for the integrator 150A to discharge fully.
  • each of which may comprise an integrator 150A or 150B, an adder 160A or 160B, a sample-and-discharge circuit 170A or 170B, or an ADC 180A and 180B, together with an input switch 145 and an output switch 185 for selecting the processing-channel.
  • Each channel takes turn to process the next incoming event.
  • This also provides an idle duty cycle for the integrators in each channel to be sampled and fully discharged.
  • This dual-channel design also allows the use of a slower ADC (50% slower) to digitize the signals thus lowering cost.
  • the digital remnant subtraction circuit 190 may include a digital look-up-table (LUT) for determining the remnant scintillation energy (from all preceding gamma rays) that the scintillator is still emitting after the arrival of the latest gamma ray.
  • the remnant subtraction circuit 190 may include a register (not shown) to store a previous weighted sum, a LUT 192 for generating an exponential term, and a digital multiplication IC (not shown).
  • the input to the LUT is the trigger-time of the present and the preceding gamma ray (actually, their time difference ⁇ t).
  • the digital energy output of the remnant subtraction circuit 190 is thus the pile- up free energy (E; ) of the detected gamma,
  • S is the weighted-sum relating to the present gamma ray
  • S is the weighted sum relating to the preceding gamma ray
  • ⁇ t is the time interval between arrival of the present and the preceding gamma ray.
  • Sj and S,- ⁇ include the remnant signals from all preceding gamma rays. This is an exact equation, regardless of how many multiple pile-ups exist in each sum signal (see APPENDIX for the mathematical justification). The correction term and the exactness of this algorithm, being independent of the number of multiple-pile-up remnants still being emitted by the scintillator, are significant consequences of the present invention.
  • the scintillation detector used in connecting with the present invention permit count-rates that produce 60% multiple pile-ups, since all the remnants from multiple pile-ups can be easily corrected for by equation (2).
  • the present invention processes all incoming events the same way, regardless of whether it is a pile-up onto a previous event or whether there is a pile-up from the next event.
  • the real-time pile-up prevention/correction provided by the present invention is an inexpensive solution to the problems inherent in the prior art. If there is no pile-up, the system converges to a conventional integrating circuit, as the sample and discharge control circuit 170 may be set to pass the resultant sum signal at a time approximately equal to Ax (i.e., approximately 1 ⁇ s for the Nal(Tl) detector discussed herein). In case of a pile-up, it correctly measures the energy of all the pile-up gamma rays.
  • a Nal(Tl) scintillation detector employing the methods and apparatus of the present invention has the potential to count up to 1 x 10 6 cps without degrading the average energy resolution.
  • a traditional detector circuit with a deadtime of 1 ⁇ s must lower the acceptable count-rate by 10 times, to 100,000 cps, to prevent the random arrival of the next gamma ray within 1 ⁇ s of the present gamma ray (Nicholson, 1974).
  • Poisson statistics shows that the non-pile-up fraction is 90% for 100,000 cps, which is why conventional Nal(Tl) detection systems cannot count over 100,000 cps.
  • the present invention can count even faster than 1 x 10 6 cps with some compromises in energy resolution.
  • the PPC of the present invention may be adapted for use with many different detectors and imaging systems.
  • the present invention may be used with thyroid probe, position sensitive detectors, or gamma ray detectors which detect neutrons, charged particles and gamma rays.
  • the conventional integration method (and its equivalent pulse-shaping method) has been the gold standard in the nuclear physics and nuclear medicine field for the past 40-50 years.
  • the present invention is a significant breakthrough. This breakthrough can be applied to many nuclear detection areas, such as nuclear physics and engineering, high energy physics, nuclear medicine, industrial gauging, and oil field down-hole logging, among others. Certain applications will be discussed presently.
  • the present invention has special attributes that make it particularly applicable to medical imaging, and especially gamma cameras.
  • a gamma ray hits a detector in a gamma camera, both energy and position information are needed for creating the image.
  • the energy information discriminates (or qualifies) the useful imaging gamma ray from background gamma rays which have been scattered around in the body being imaged (scattering lowers the gamma energy).
  • the position information locating the point of detection of the gamma ray has to be determined to create a gamma ray map (image).
  • the pile-up prevention circuit (PPC) of the present invention can determine the gamma ray energy, despite pile-ups. However, the present invention would be less useful for gamma cameras if it could not also determine the gamma ray position in pile-up situations.
  • a particular embodiment of an apparatus according to the present method may be incorporated into a regular gamma camera to determine position information, as well as energy information in a pile-up situation.
  • This embodiment may be known as a position-energy pile-up prevention (PEPP) algorithm and circuit.
  • PEPP position-energy pile-up prevention
  • This solution is compatible with existing gamma camera electronics. Compatibility is important because it allows the pile-up-prevention circuit of the present invention to be applied to present gamma cameras without major modification to their existing front-end electronics.
  • a regular gamma camera and its electronics generate five signals of interest for the present invention, namely X + , X_, Y + > Y_, and Z.
  • Z is the energy of the gamma ray.
  • X-position and Y-position of the gamma ray can be calculated from these five signals
  • the same PPC circuit may be applied directly to the prenormalized position signals, X' and Y', to prevent pile-ups by generating pile-up-free X' and Y'.
  • the mathematical proof of this property can be found in the APPENDIX.
  • the PPC circuit of the present invention may be connected to the prenormalized positioning signals X' and Y' in a regular camera, as well as the energy signal Z' (a fast instantaneous signal sum of all the PMT's), as shown in FIG. 6, to generate three pile-up-free signals X, Y' , and Z' for calculating the energy and position of the detected gamma ray despite multiple pile-ups.
  • the system of FIG. 6 includes a conventional gamma camera 200, which develops prenormalized position signals X' and Y', and energy signal Z'. Each of these signals is input into a separate pile-up prevention circuit (PPC) 210.
  • PPC pile-up prevention circuit
  • This PPC 210 may be the same circuit as discussed above, in connection with FIGS. 5 A or 5B, or it may be a slightly modified version (as shown in FIG. 6, certain components of the circuit of FIG. 5 A have been deleted for illustrative purposes).
  • First the PPC 210 may not have a time trigger, as trigger signals for this embodiment may come directly from a fast trigger 220, which is input to all of the PPC's 210.
  • This fast trigger 220 is a new addition to a conventional gamma camera.
  • the individual PPC's 210 may not have a remnant subtraction circuit, as all signals output from each PPC 210 maybe input into a digital signal processor (DSP) 240.
  • the DSP 240 may include the remnant subtraction algorithm for the X', Y', and Z signals.
  • the DSP 240 provides for faster processing. However, in certain embodiments, it may be possible to have the lookup tables within the individual PPC 210 units.
  • the DSP 240 may also include other corrections (energy and distortion corrections) for the X', Y' and Z signals, and X, Y renormalization process.
  • the system of FIG. 6 also includes a coincidence timer 230, which receives a trigger signal from the fast trigger 220. Upon receipt of the signal, the coincidence timer 230 sends a time clock signal to FIFO's 235, which is transmitted to the DSP 240. This time clock signal is for pile-up remnant subtraction and for coincident timing measurement in positron coincidence imaging (PET).
  • PET positron coincidence imaging
  • the prenormalized position signals (X', Y') obtained from gamma camera 200 are delayed, amplified, and integrated within the PPC 210.
  • the amplified instantaneous position signals ⁇ X'(t) and ⁇ Y'(t) are summed to their integrated position-signal, ⁇ X' (t)dt, ⁇ (t)dt, respectively, also within the PPC 210.
  • These weighted sums of prenormalized positions are immediately sampled by a fast analog-to-digital converter (ADC) within PPC 210, just before the onset of the next pile-up event.
  • ADC analog-to-digital converter
  • the arrival of the next gamma ray is sensed by the fast trigger 220, which monitors the fast instantaneous total energy output, Z
  • the integrator circuit of PPC 210 is immediately discharged so that it can start integrating the position signals coming from the next pile-up gamma ray.
  • the fast trigger 220 also marks the arrival time of all gamma rays.
  • the timing mark is generated by a fast clock, which in an exemplary embodiment may be a 250 MHz clock.
  • These arrival times are sent to the DSP 240 for remnant signal subtraction and for positron coincidence detection in PET imaging.
  • the remnants of position signals, generated by the residual light output of all preceding pile-up gamma rays, will be subtracted from the present position weighted-sum in the DSP 240 in FIG. 6 using a LUT that stores the exponential term in the following remnant subtraction operation to determine the remnant position signal to be subtracted from the ;-th event:
  • the DSP 240 also performs the regular correction processes for linear distortion, field nonuniformity, and regional signal-pulse-height variation, in real time.
  • the host processor 250 is for image display and operator interface.
  • An apparatus thus decodes the position and energy of each detected event.
  • the fast trigger 220 detects the arrival of an event, and triggers a time-mark output in the coincidence-timer 230 for the event's arrival time. This event-arrival time mark will be used to calculate the prenormalized positions and energy.
  • the calculation may be performed by the DSP 240, where exponential functions may be stored as a look-up-table.
  • the DSP 240 also performs the energy normalization on the prenormalized positions to provide the true position signals. In this processing scheme, all the events (photopeak or true events, and scatter noise events) are included in the processing to calculate all the remnant signals from previous events, and an event's real energy is not known until after processing.
  • the energy acceptance of an event has to be made after the decoding operation, in/after the DSP 240. If the decoded energy is higher than that of the scatter radiation noise signal, the detected radiation is accepted as a true (photopeak) event.
  • the output of the DSP is thus the pile-up-free, energy-normalized positions (x, y) and gamma-energy (z). Since all data acquisition computers in gamma cameras accept the standard signals of (x, y, z), the proposed processing algorithm and electronic architecture is compatible with existing data acquisition computers. This compatibility is useful to adapt the scheme to existing cameras. Implementation of the present invention in a conventional camera is very feasible, as shown in FIG. 6.
  • a DSP circuit is standard in most cameras for processing position signals and for distortion correction.
  • the only additional circuits needed for incorporating the methods of the present invention into a regular camera are the three channels of PPC circuits according to the present invention, a fast trigger circuit, and a clock, which increase production costs by only a few hundred dollars to achieve a 10-20 times increase in count-rate capability.
  • the present invention also provides for further improvement of the detection rates of a gamma camera.
  • the camera signals may be split geometrically into 4 or more independent signal processing zones as if four independent cameras existed adjacent to each other. More specific details of such a system are disclosed in U.S. Patent No. 5,319,204 and, U.S. Patent No. 5,453,623, the disclosures of which are hereby incorporated by reference.
  • the incorporation of the PEPP (position and energy pile-up prevention) algorithm of the present invention into such a multi-zone design would further increase the count-rate capability of the camera by two or three times.
  • Multi-zone designs have been proposed and implemented in NaI(Tl)-based PET cameras to increase maximum count-rate capability (Muehllehner et al, 1995; Muehllenhner and Karp, 1986; Karp et al., 1986; Freifelder et al, 1994). These designs depend on the fact that most of the scintillation light is distributed only to the neighboring 7-9 PMTs.
  • the camera may be divided into four identical square zones, identified as K, L, M, N, as shown in FIG. 7. Each zone therefore has nine PMT's (3 x 3). Each zone may be treated as an independent camera with its own PEPP circuit according to the present invention to correct for pile-ups and image distortions.
  • the nine PMT's in each zone may be grouped into one signal-triggering line. With four zones, there would be four signal-triggering lines, S , S , S M , S N . If the first gamma ray is detected in zone
  • the PEPP circuit of zone K would be turned on to measure its position and energy. If a second gamma is detected in zone K within the pile-up time, the PEPP circuit would correctly measure the position and energy of both gamma rays.
  • zone L If the second gamma ray strikes zone L while zone K is processing a prior count, two scenarios may occur. These two scenarios are addressed in detail:
  • the gamma rays detected in zone K and zone L are both far from the zone boundaries between K and L, such that there is little light spilled from one zone to the next. Hence, there is little or no signal interaction between the two events to cause positioning errors. Both gamma rays may be processed independently by the PEPP circuit of each zone to obtain the correct energy and position.
  • the first gamma ray detected in K is so near the K-L boundary that the PEPP circuits in both zone K and zone L are triggered, as shown in FIG. 8.
  • zone K may decode a valid position, but zone L would decode an artifact-count at the K-L boundary near the event in K, as shown in FIG. 8.
  • the remnant signal of the fictitious count created in the L-PEPP circuit would be subtracted from the signal of the second gamma ray (A), so that there is no interference in determining the position of the second gamma ray.
  • both the first (K) and second (L) gamma rays would be correctly measured, but an additional artifact count will be created at the K-L boundary.
  • each zone may have its own PEPP circuit 310.
  • each zone may have its own DSP 315.
  • the interzone coincident detection circuit receives input from the fast timing triggers of each of the zone PEPP circuits 310.
  • the multi-trigger processor 340 receives zone position signals from each of the zone PEPP circuits 310.
  • the processor 340 may be a DSP.
  • the output of processor 340 is input into a main DSP processor 350, which provides information to image buffer 360, interface 370 and Host CPU 380.
  • the main DSP processor 350 serves two functions: (1) it merges the four zone-images into one image, and (2) it performs a final distortion correction for the combined image.
  • the interzone coincidence-triggering circuit 330 may be used to detect the simultaneous triggering of two or more zones caused by an event detected near the boundary.
  • the PEPP circuit 310 in each zone would respond (as originally designed) as if an independent event is detected in each zone by generating their own position signals,
  • the simultaneous triggering of both zones would also activate the inter-zone coincidence circuit 330 which would then feed these two or more independent position signals into multi-zone-trigger processor 340, which performs a centroid averaging for these two or more position signals.
  • this averaging is equivalent to combining the two or more zones and using the regular Anger positioning method over this larger domain, as shown in the following equation:
  • This averaged position is stored in the main processor 350 that stores the composite camera image (four zones combined), whereas the individual zone position signals (X ⁇ and X ⁇ ) are discarded.
  • This method thereby eliminates the boundary-artifact event and also provides a better estimation of the position, since all of the scintillation light emitted would be used for computing the position (including light spilled into the adjacent zone).
  • Inter-zone light spill also exists in the two high count-rate cameras using a multi-zone design because, as long as a single NaI(Tl) crystal is used, light will be distributed from one zone to the next.
  • Technical solutions are readily achievable as indicated by AD AC MCD and UGM SPECT and PET cameras (Muehllehner et al, 1995; Glass et al, 1996; Freifelder et al, 1994).
  • the present invention, using a monitor to detect coincidence triggering of two zones is simple, straightforward to implement, and usable with the pile-up prevention technology of the present invention.
  • FIG. 19B Shown in FIG. 19B is a flow chart for the method of the present invention relating to this multi-zone pile-up prevention embodiment.
  • an instantaneous detected signal is provided to four independent PEPP's in step 410. Then it is determined whether this signal creates a multi-trigger event in step 420. If it is not a multi-trigger event, control passes to step 430, in which it is determined whether it is a single-trigger event. If it is a single-trigger event, control passes to step 440 and single active zone position processing is performed, as discussed above.
  • step 450 active zones are combined into a larger domain for processing. Then, the large domain position processing is performed in step 460, as discussed above. The result of either path of this method results in a determination of the true and accurate position of the instantaneous signal in step 470.
  • scintillation detectors can be divided into four main areas:
  • a new and potentially important application of the present invention is in airport surveillance to look for plastic explosives in luggage using, for example, neutron activation techniques.
  • the ability to detect radiation 10-20 times faster would allow (a) detectors to be used in a much higher radiation areas to extend the usefulness of the detector system, (b) the ability to count faster would increase the speed of data acquisition to shorten the data collection time, e.g., in an airport bomb surveillance system, a 10-20x stronger neutron source can be used to scan luggage faster, so that luggage scanning times can be reduced by 10-20 times to improve throughput.
  • the scintillation detector is used in conjunction with radiation sources to measure the quantities or density of materials being processed.
  • a nuclear level gauge may be used to stop the pouring process when a specific level is reached.
  • Another example is "thickness gauges" using gamma-ray backscatter detectors in thin-film processing in the plastic and paper manufacturing industry (especially for high-value films such as video-tapes and electronic capacitor films). Quite often, the film to be scanned is manufactured in large-area sheets, and the detectors together with the radiation source must scan the entire sheet.
  • the detector's ability to detect gamma rays at very high count-rate (10-20x) means that a very intense gamma-ray source (10-20x) can be used, which in turns translates to a 10-20x faster data acquisition.
  • the time spent on the inspection-scanning processes or manufacture-control processes can be reduced by 90%, thereby increasing production rate.
  • Scintillation detectors are also widely used in radiation monitoring in nuclear reactors, and in oil field borehole logging to survey rock/hydrocarbon structures along the borehole in oil exploration. A faster counting system would increase the information collected or decrease the data collection time, which would lower the cost of data acquisition (oil rig time is very expensive).
  • Scintillation detectors are also widely used for nuclear applications, for example: (a) reactor monitoring of liquid and gaseous streams to look for isotopes, (b) fuel rod cladding failure, (c) isotope scanning for irradiation fuel to determine power distribution and migration of fission products in the reactor core, (d) reactor fuel fabrication and quality control, (e) spent fuel reprocessing, and (f) management of nuclear waste. Since these nuclear-reactor related detectors are used in very high radiation flux areas, this high count-rate invention is potentially very useful in the nuclear energy business.
  • positron imaging which exposes the Nal(Tl) detector to a 10-fold or more gamma-ray flux, with the removal of the lead collimator from a gamma camera for positron imaging;
  • the count-rate capability of gamma cameras can be enhanced by 20-40 times, which would allow (or improve upon) the above useful imaging protocols.
  • the new capability may reduce reliance on the use of PET costing $2,600,000 to purchase and
  • Another application of the present invention is for the low-cost, high- resolution PET detection system of PMT-quadrant sharing design, as shown in U.S. Patent Nos. 5,319,204 and 5,453,623, to compensate for its lower count-rate.
  • the present invention will open up new and exciting clinical applications for gamma cameras, which is especially important in today's healthcare environment when clinics must perform more with less money.
  • HYPER method thereby either improving the energy and position resolution or increasing the processing speed for pile-up prevention techniques.
  • This disclosure also introduces a zone- identification methods for the application of multiple HYPER circuits to further increase the count-rate in gamma and PET cameras. It also explains how to use the HYPER method in the
  • the HYPER method involves a set of formulae that solve the signal pile-up problem in scintillation detectors for both energy and position signals despite the pileup of multiple signals.
  • the spirit of the methodology is as follows: (a) dynamic integration - the signal integration triggered by a present-event stops immediately before the next event is detected; (b) calculating a 0 weighted value for estimating a total energy in the scintillation, which includes the energy of the current event and a residual energy from all the previous events; and (c) remnant correction is used to calculate a pile-up free energy from two consecutive weighted values.
  • the above three steps may be used to create a pile-up free signal.
  • This disclosure explains several ways to implement and to improve the measured resolution of the weighted 25 value for estimating the total energy by: (1) applying an analog filter to the weighted-sum of an instantaneous value and an integrated value; the weighted-sum signal is multiple sampled, and another digital filter may be applied to those samples to get a better weighted value; (2) dynamic, digital weighting the integrated value; (3) dynamic weighting the sum of the multiple-sampling (repeated sampling) of the values of the instantaneous signal.
  • a dynamic integrating method is used, which means that the measured energy and position signals of the present-event are no longer synchronized with the trigger. This is the case because the energy and position signals of the present-event are measured at the arrival-time of the next-event (at a random time), and the trigger is issued at the arrival time of the present-event.
  • the original trigger signal may be delayed, and a new synchronization may be setup between the trigger and the energy or position signals before they go to a coincidence procedure.
  • the improved HYPER method, multiple HYPER zones method, and this synchronization method may all facilitate the use of PET for applications such as, but not limited to, positron imaging, gamma cameras for radionuclide therapy, dosimetry imaging, cardiac first- pass imaging, positron coincidence imaging, and the simultaneous acquisition of transmission and emission data using difference isotopes with less-contamination between transmission and emission data.
  • Every exponentially decreasing pulse signal for example from a scintillation detector, includes a present pulse signal and a remnant signal from all the previous pulse signals.
  • the total light signal after event 4 is the sum of the light signal of event 4 and a remnant light signal.
  • S n the total energy inside the detector after event-n without post-pileups
  • E n the energy of the event n
  • R n the remnant energy from all the previous events
  • ⁇ the decay time
  • PX n+l3 PY n + ⁇ are the pileup-free pre-normalized position signals for event (n+1) and SX n + SY n+ ⁇ are the total estimated pre-normalized position signals.
  • the present disclosure in a broad aspect, comprises a dynamic pileup prevention technique for increasing the count-rate capability of Anger type cameras with scintillation detectors such as, but not limited to, NaI(TI), BGO, GSO, LSO, plastic, and Csl.
  • the dynamic pileup prevention technique has a variable detector signal collection time (deadtime), whereas conventional systems typically have a fixed deadtime (4 ⁇ , 1 ⁇ s for Nal scintillator).
  • the integration of the first event stops immidiately if the next event is detected with a certain period of time (AT).
  • FIG.20 shows an exemplary diagram of an appropriate circuit.
  • the computation circuit in FIG. 20 calculates a total value of a first and second incoming pre-normalization signal and a third incoming energy signal.
  • Equation (2.4) indicates that the weighted-sum signal of the integrated signal and the instantaneous signal amplified by T is a constant.
  • the weighted-sum signal is always a measure of the total radiation energy before the next event is detected, regardless of when the sum-signal is sampled. Since the instantanous signal is more noisy than the integrated signal, a low-pass smoothing circuit may be applied to the weighted-sum signal to reduce the noise. To further increase the signal to noise ratio, the weighted-sum signal may be multiple/continously sampled, and a digital filter maybe applied to the samples to get a better estimated value.
  • the filter may be a median value filter or a weighting output of these samples.
  • SRON + W 2 S n 2 + ... + W m S" , where S law' indicates the i-th sample of the weighted-sum signal S n may be used.
  • FIG. 24 shows a diagram of an appropriate decay filter.
  • the number of samples (N) is not fixed.
  • the accumulated output signal maybe normalized by: ⁇ _ -N*hT/ ⁇
  • Equation (2.5) indicates that the total estimated energy may be calculated by weighting the integrated value (integrating the pulse signal from t n to t n+1 ).
  • the weighting factor may be defined by the time lapse between the two events n and n+1.
  • One possible disadvantage of this method is that the system needs good timing resolution because the weighting factor is sensitive to time resolution — especially with a small time lapse. Additionally, it may need a real-time calculation or a look-up-table to generate the result.
  • Digital integration means the instantaneous signal is continuously sampled, and the samples of each event are accumulated in digital form. Unlike analog integration, there is no dead-time of integration discharging for digital integration. However, this method requires a fast analog to digital converter and a digital accumulator. The rest of the calculation for estimated total energy is the same as described above — the accumulated value may be weighted by a factor that is defined by a time lapse of two countinuous events.
  • Remnant correction is an important step in creating a pileup-free signal, especially for multiple/continuous pileups.
  • the residual signal is subtracted from the total estimated energy.
  • the residual term may not be a small correction, and without the residual- subtraction, the weighted value may be larger than the real energy of the present event by two times or more since the preceding pulse can itself be riding on several orther earlier signals, which makes the proceeding weighted value much larger than the energy of the preceding signal and the energy of the present signal.
  • a remnant signal may be created by weighting the S n+ ⁇ with a factor exp(-T n+1 / T), which may be given by a look-up-table (LUT) of T n+ i . This remnant signal may be stored in a register for the residual correction of the next event.
  • FIG. 23 illustrates this.
  • the look-up-table (LUT) gives the weighting factor of -
  • All the remnant signals (from multiple pileups) that goes to the next event may be generated by subtracting the integrated value from the total estimated value. This remnant signal may be stored in a register and used for the residual correction of the next event.
  • Some detectors emit signals that follow two or more exponential decay-time constants. In these instances, the extractions of pileup-free energy and position may be more complicated. The same general methodology of the common mono-exponential case as described above, however, may be used. Each integration may be sampled twice (or more) over the cause of integration. The additional sampling provides another set of equations to derive the relative magnitutes of the two (or more) exponentials in the total energy (present event plus remnants). Even though for an isolated event (non-pileup), the relative magnitutes for the event are constant and known, the remnant energy in a pileup case will have different relative magnitutes for the two exponentials depending on the time-lapse between consecutive events. The additional samplings allow one of ordinary skill in the art to derive the relative strengths of the exponential.
  • High resolution time measurement may be an important issue for pileup processing.
  • a counter with a regular resolution (for example 12ns) combined with a high resolution delay line (for example, Ins resolution) may be used to measure the time lapse in high resolution.
  • Ins resolution For example, Ins resolution
  • An embodiment of this disclosure is to use a slow clock to measure the time lapse to get a raw time T m .
  • T m is 7 cycles of the slow clock.
  • the rising edge of each event changes the status of a 'flag' signal (from 'high' to 'low', or from 'low' to 'high').
  • This flag signal inputs into a delay line with multiple tap outputs, which has, for example, a 1 ns time delay difference between two continuous taps.
  • the rising edge of the first clock after each event-trigger latchs the delay line outputs.
  • To measure the time Td n between the rising edge of the 'flag' signal and the first clock signal one may count the number of delay line taps with 'high' output. This number multiplied by the tap delay step (Ins) is the time Td n (10ns in FIG. 28).
  • the same methodolgoy may be used to measure the time Td n+1 between the falling edge of the 'flag' signal and the following first clock — one may count the number of delay line taps with 'low' output and multiply by the tap delay step, hi FIG. 28, this is 3ns.
  • this methodology involves determining an approximate time between the two consecutive events using a first clock. Then, a first and second correction to the approximate time is determined using a second clock, the second clock having a finer time resolution than the first clock. Finally, the time between two consecutive events is found by applying the first and second corrections to the approximate time.
  • multiple HYPER zone circuits may be implemented.
  • a detector may be divided into a plurality of smaller HYPER zones by grouping PMTs into multiple smaller Anger cameras in electronics.
  • Some PMTs may be shared by two or more HYPER zones. Events collected by shared PMTs may trigger two or more HYPER circuits at the same time.
  • FIG. 25 shows a detector divided into four zones (zones K, L, M and N). Since every two neighbor zones share one row or one column of PMTs, one gamma hit may trigger two zones if its energy is collected by the shared PMTs. To find out the zone that has the "real" hit, a threshold may be set for the pre-normalized position signals of each zone to reject the false hit from its neighbor zone.
  • FIG. 26 shows an example of a two-zone design. Each zone has one independent block detector coupled to 4 PMTs.
  • a "real" hit in a zone should pass both the energy-acceptance threshold and pre-normalized position-acceptance threshold, which in this example would be about 3-6% of E0 (the zonal energy-acceptance threshold).
  • E0 the zonal energy-acceptance threshold
  • a false hit caused by its neighbor's zone may be accepted by the energy threshold but it will not be accepted by the pre-normalized position threshold that is set to 3-6% of E0.
  • the HYPER method combined with multiple zones may significantly increase the count- rate capability and dose efficiency of PET and gamma cameras.
  • coincidence detection applications and other timing-detection applications such as positron coincidence imaging, a special additional technique is provided.
  • the signal integration time for each event is fixed. Therefore, the end of integration and signal digitization (for energy and position) is synchronized with the trigger signal (delayed by the fixed integration time).
  • the trigger signal is generated at the leading edge or the arrival time of the event.
  • Coincidence detection may be performed between the end of digitization signals or the trigger signals.
  • the HYPER uses a dynamic integrating method, which means that the measured energy and position signals are no longer synchronized with the leading-edge of the present triggering signal because the energy and position signals are generated or digitized at the arrival of the next event (arriving at a random time from present event).
  • the original trigger signal may be delayed by a fixed time, and a new synchronization process may be setup between the delayed trigger and the energy/position signals before they go to a coincidence procedure.
  • the synchronization process works as follows.
  • the energy and position signals of all events may first be buffered into a FIFO (first-in-first-out) temporary memory.
  • a delayed trigger signal may be used to read them out individually. Since the readout of the energy and position signals from the FIFO queue is time-latched by the delayed trigger, and since the delayed trigger signal is synchronized with the trigger signal (except for the fixed delay-time shift), the energy and position signals may be synchronized to the trigger signal. This is shown in FIG. 27.
  • the fixed delay time should be longer than the maximum integration time.
  • the trigger- delay circuit should have a good time resolution and a small dead time since the delayed trigger signal is synchronized with the trigger signal (except for the fixed delay-time shift).
  • the units for time are microseconds.
  • the event integration (sampling) time is the next event's arrival time if the current event is piled-up by the next event. If there is no pileup on the current event, it will be integrated for a fixed maximum time period. In this example, 1 microsecond was used.
  • the waiting time is the time difference between the FIFO readout time and the event input time.
  • the order of the data in a FIFO is the same as the order of events arriving. Hence, the linear structure of the FIFO is used to line up all the events in the order that they arrive. Then, a large fixed delay (larger than the longest integration time) is applied for the event-trigger, and the delayed event trigger is used to "clock" the readout of events from the FIFO. Hence, each event in the FIFO may be clocked out (readout) synchronously with the event triggering time (exact for a fixed delay). It is the waiting (holding) time of an individual event in the FIFO (as controlled by the delayed trigger) that synchronizes the FIFO readout time to the original event-arriving time.
  • the present invention was used in connection with a 3"x 4" Nal(Tl) scintillator with a photomultiplier from Ortec Corporation (Oak Ridge, . TN).
  • This detector was connected to (1) regular detector electronics setup using a pulse-shaping amplifier (0.5 ⁇ s shaping time) and a multi-channel analyzer, and (2) to the pile-up prevention circuit ("PPC") of the present invention.
  • PPC pile-up prevention circuit
  • the circuit may be interfaced to a computer.
  • the present invention was connected to a PC computer with a 133 MHz PENTIUM processor and a high-speed input/output board for the studies.
  • the data acquisition software was written with LABNEEW (National Instruments, Austin, Texas).
  • a 99m Tc point source (140 KeN gamma ray) in air was used for all the count-rate studies.
  • the pile-up-prevention circuit of the present invention may also be used to measure the number of nonpile-ups, single pile-ups, and multiple pile-ups.
  • circuits implementing three methods were setup and tested.
  • the methods included: (i) the pulse-shaping method (500ns); (ii) delay-line clipping (256 ns); and (iii) the method according to the present invention.
  • the pulse-height spectra, energy resolution and acquired true-count fractions were collected as a function of true-even rates using a 99m Tc (140 KeN) point source, which decays with a 6 h half-life. This half-life was used to calculate the true-even rate impinging the detector when very high count-rate data were acquired.
  • FIGS. 12A and 12B show results of the pulse-shaping method
  • FIG. 12A show results of the pulse-shaping method
  • FIG. 12B show results of the present invention.
  • the pulse-shaping method (FIG. 12 A) started to demonstrate pile-up at the higher energy side and distortion at the lower energy side. Above 200-300 Kcps, the spectra were not usable.
  • the PPC method spectra (FIG. 12B) maintained the spectra shape even at 2 Mcps.
  • the method of the present invention was compared with a delay-line clipping (DLC) experimental setup (using NIM electronic modules and a 256 ns clipping).
  • the energy resolution results are shown in FIG. 14.
  • the PPC method had better resolution than the DLC method, while at 2 Mcps the energy resolution was about the same.
  • the study also generated the photopeak-count rates, .i.e. the non-pile-up good counts acquired by each method using a narrow energy window, as a function of true-count rates, as shown in FIG. 15.
  • the photopeak counts were 85% of the total incident counts, while the DLC had only 25% good counts.
  • the low photopeak fraction in the DLC method was due to a high 75% count-loss due to pile-ups which placed the pile- up-event energy above the photopeak acceptance-window.
  • the DLC method delayed the occurrence of pile-up due to its shorter pulse width, but at very high count rates, its fixed pulse-width still made it more vulnerable to pile-ups (FIG. 16) than the PPC method, which has a variable signal-integrating time and count-recovery capability.
  • the photopeak counts collected by the PPC method is 3.3 times more than the DLC method at 2 Mcps.
  • the pulse-shaping method only maintained 35% at 0.25 Mcps, and there was no useful photopeak data above 0.25 Mcps because of pile-ups (FIG. 15).
  • FIGS. 17A-F The importance of an effective remnant light subtraction for every triggering event is demonstrated in FIGS. 17A-F, especially at very high counting rates.
  • SWS simple weighted-sum method
  • Mcps the energy measurement errors of SWS are significant. Above 2 Mcps for Nal(Tl), most events are riding on the signal of other events (see Table 2 and FIG. 16), and SWS would measure large energy errors on most events and cause severe count-loss outside the photopeak acceptance window.
  • the SWS energy measurement errors demonstrated here should be similar to that shown in U.S. Patent No. 5,430,406 discussed above.
  • FIGS. 15-17 demonstrates the count and energy recovery/restoration capabilities of the present invention.
  • FIGS. 18A-C a Monte Carlo simulation of the torso (with liver, kidneys, and bladder) was performed to demonstrate the effect of pile-ups in imaging at 2 Mcps for: (a) the method of the present invention (FIG. 18A); (b) the pulse-clipping method (256 ns) (FIG. 18B); and (c) the regular fixed integration method (1 ⁇ s) (FIG. 18C).
  • the study simulates the electronic processing of each method in a gamma camera.
  • the results are shown in FIGS. 18A- C.
  • the present invention method showed all the uptake organs; the conventional method shows no organs; the pulse-clipping result was in between the two, with high pile-up artifacts between the two kidneys and diminishing activities in the bladder and kidneys.
  • the present invention allows data acquisition time to be shortened significantly. This fast data acquisition is important in commercial/medical applications, as data acquisition time can be significantly reduced.
  • the count loss with the conventional method is very high above 160,000 cps and saturates at 200,000 cps.
  • the pile-up fraction at this limit is very large, and the photopeak is badly distorted. Therefore, a large percentage of the data is not useful.
  • the present invention can count over 2,000,000 cps with very little count loss, while preserving a very good photopeak, and all of the data is useful.
  • the present invention is a significant improvement over the prior art.
  • the PPC energy resolution is the same as the standard pulse-shaping method.
  • the PPC energy resolution only degraded slowly from 10.9% at 50 Kcps to 15% at , 2000 Kcps.
  • the PPC method has better energy resolution at regular count rates (10.9% vs. 15%) and 3.3 times higher photopeak (non-pile-up) counts at 2000 Kcps.
  • the count and energy recovery capability of the present invention at very high count rates is important for extending the maximum count rates of scintillation detectors.
  • a 7-th gamma ray ( ⁇ j ) is detected.
  • the y ' -th gamma ray is a pile-up event on top of two preceding gamma rays ⁇ j - ! and ⁇ j . 2 .
  • the instantaneous scintillation emission of a scintillator after detecting a gamma ray is
  • E is the total scintillation signal generated by the scintillator, and E is proportional to the energy of the gamma ray detected.
  • the instantaneous signal at time tj for t j ⁇ t ⁇ t j+1 contains emission from three gamma rays ⁇ j - 2 , ⁇ j -i, ⁇ j , and is given by,
  • the weighted sum for this period is:
  • the energy deposition of the j-th gamma ray can be derived from they ' -th weighted sum minus the preceding weighted sum decreased by a emission decay factor, provided that the integrator is discharged immediately before the arrival of they ' -th gamma.
  • the weighted-sum S is not a measurement of energy of they ' -th event, it is the measurement of the total energy trapped inside the scintillator just after the /-th event hit; i.e., Sj includes the energy of they ' -th event and all the remnant energy of previous multiple-pile-ups when the -th event is deposited.
  • Equation (9) is an exact solution, regardless of how many previous gamma tails on which the -th gamma is riding.
  • the present invention thus provides the first method that attempts to recover all triggering events and compensating for multiple-pile-up exactly.
  • the present invention may achieve higher count rates than possible with known methods.
  • Equation (9) can be easily understood intuitively. If there is no pile-up, S j is the detected energy of they ' -th gamma ray (independent to when S j is sampled). If there are pile-ups, S j is the total energy in the detector in they ' -th period (independent to when S j is sampled), which includes the detected energy of the/-th gamma ray and the remnant emission of all the preceding gamma ray. Thisj ' -th remnant emission is simply the total energy in the preceding period (S j -i) decreased by the emission decay factor governed by the time difference between the -th gamma and its preceding gamma.
  • E,- is the total signal received by Photomultiplier-i (PMT-i) when a ⁇ -ray is detected
  • X is the physical location of PMT-i.
  • X is the prenormalized pseudo-position signal which needs to be normalized by the total detected energy Z of the ⁇ -ray, to generate the centroid location X can be defined as:
  • the total energy (after signal integration) distributed to PMT-1, PMT-2, . . . , PMT-n are E n , E n , . . . , E ln , respectively.
  • the total integrated energy detected by the camera is:
  • Equation (12) In conventional Anger-position, E;, in equation (12) are the integrated PMT signals (integrated for 0.6-1 ⁇ s), and therefore X ⁇ in equation (12) is a static quantity obtained after a fixed 1 ⁇ s integration time. Hence, if there is a pile-up during the integration time, X ⁇ will be wrong.
  • the instantaneous prenormalized position X(t) is used:
  • the weighted instantaneous prenormalized position is:
  • the integrated prenormalized position is:
  • the prenormalized position weighted sum will not be equal to the true prenormalized position of ⁇ ls because SX[ contains the remnant prenormalized position weighted-sum SX 0 ' generated by the remnant scintillation of ⁇ 0 .
  • the ⁇ 0 remnant position weighted-sum adds an error-position vector to the j ⁇ position. The magnitude of this error vector increases if the time lapse (tj-to) between ⁇ 0 and ⁇ ! decreases.
  • the weighted instantaneous prenormalized position signal triggered by an incident event ⁇ m is given by the superposition
  • This integration can be carried out by first zeroing the integrator just before the onset of ⁇ m , and then restarting the integration immediately.
  • the prenormalized Anger-logic position (X' m , Y'm ) of ⁇ m can be derived from the weighted prenormalized position sums of ⁇ m , m - ⁇ , and the time-lapse between the two events,
  • equation (20) Since the derivation of equation (20) assumes that ⁇ m is riding on any numbers of preceding events, equation (20) provides an exact determination of the position of ⁇ m , even when it is part of a multiple-event pile-up.
  • the pile-up-free prenormalized position (Xm, Y'm ) will then be renormahzed by the energy of ⁇ m as in conventional Anger-logic to remove the energy-scaling effect in generating the position of ⁇ m -
  • the energy of ⁇ m also has to be extracted correctly from a multiple-event pile-up if the position of ⁇ m is to be decoded accurately.
  • the pile-up-free energy of ⁇ m can also be derived from the energy weighted-sum of ⁇ m , ⁇ m - ! , and the time lapse between these two events,
  • S is the sum of the weighted instantaneous scintillation signal and the integral of the instantaneous scintillation signal.

Landscapes

  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Medical Informatics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Molecular Biology (AREA)
  • Engineering & Computer Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Biomedical Technology (AREA)
  • General Health & Medical Sciences (AREA)
  • Radiology & Medical Imaging (AREA)
  • Surgery (AREA)
  • Animal Behavior & Ethology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Pathology (AREA)
  • Biophysics (AREA)
  • Nuclear Medicine (AREA)
  • Measurement Of Radiation (AREA)

Abstract

L'invention concerne des procédés et des dispositifs permettant d'obtenir des données sur la position et sur l'énergie sans qu'il y ait accumulation des signaux. Un procédé de l'invention consiste à interrompre l'intégration des signaux, déclenchée par un événement en cours, lorsque l'événement suivant est détecté, puis à calculer une valeur pondérée permettant d'estimer l'énergie totale dans une scintillation, cette valeur comprenant l'énergie de l'événement réel et une énergie résiduelle issue des événements précédents. Le procédé utilise ensuite une opération de correction pour calculer une énergie libre accumulée à partir de deux valeurs pondérées consécutives. Un filtre analogique peut être utilisé pour réduire le bruit. Le traitement des données peut faire intervenir une opération de pondération numérique dynamique des valeurs intégrées et/ou une intégration numérique. L'accumulation peut être évitée conjointement avec divers types d'application, y compris des applications de détection multizones et des applications de détection de coïncidences. L'invention concerne également des techniques de synchronisation à haute résolution, permettant d'empêcher l'accumulation des signaux.
PCT/US2002/032788 2001-10-16 2002-10-16 Procede et dispositif permettant d'empecher l'accumulation des signaux WO2003040757A2 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP02799158A EP1444534A2 (fr) 2001-10-16 2002-10-16 Procede et dispositif permettant d'empecher l'accumulation des signaux
CA002463756A CA2463756A1 (fr) 2001-10-16 2002-10-16 Procede et dispositif permettant d'empecher l'accumulation des signaux

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US09/981,681 2001-10-16
US09/981,681 US6936822B2 (en) 1997-05-07 2001-10-16 Method and apparatus to prevent signal pile-up

Publications (2)

Publication Number Publication Date
WO2003040757A2 true WO2003040757A2 (fr) 2003-05-15
WO2003040757A3 WO2003040757A3 (fr) 2003-11-27

Family

ID=25528573

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2002/032788 WO2003040757A2 (fr) 2001-10-16 2002-10-16 Procede et dispositif permettant d'empecher l'accumulation des signaux

Country Status (4)

Country Link
US (1) US6936822B2 (fr)
EP (1) EP1444534A2 (fr)
CA (1) CA2463756A1 (fr)
WO (1) WO2003040757A2 (fr)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008050283A3 (fr) * 2006-10-25 2008-07-10 Koninkl Philips Electronics Nv Appareil, dispositif d'imagerie et procédé pour détecter un rayonnement de rayons x
WO2009121131A1 (fr) * 2008-03-31 2009-10-08 Southern Innovation International Pty Ltd Procédé et appareil de diagraphie de forage
JP2012088306A (ja) * 2010-10-19 2012-05-10 Toshiba Corp Ｐｅｔ検出器モジュール、放射線検出器、ｐｅｔスキャナシステム、信号処理方法、及び放射線検出器モジュールの製造方法
WO2012101332A1 (fr) * 2011-01-27 2012-08-02 Michel Tararine Procede et dispositif de correction d'empilement d'impulsions pour un detecteur de rayonnement
WO2013014132A1 (fr) * 2011-07-26 2013-01-31 Multix Sa Dispositif et procede de traitement pour une mesure spectrometrique d'un flux de photons
US8471210B2 (en) 2008-03-31 2013-06-25 Southern Innovation International Pty Ltd. Radiation imaging method with individual signal resolution
EP2461183A3 (fr) * 2010-10-19 2014-05-21 Kabushiki Kaisha Toshiba Module détecteur de tomographie à émission de positrons, détecteur de radiations, système de balayage de tomographie à émission de positrons, procédé de traitement de signaux et procédé pour la fabrication du module détecteur de radiations
US8812268B2 (en) 2008-12-18 2014-08-19 Southern Innovation International Pty. Ltd. Method and apparatus for resolving piled-up pulses by using a mathematical transform
WO2014132003A1 (fr) * 2013-02-28 2014-09-04 Commissariat A L'energie Atomique Et Aux Energies Alternatives Dispositif de traitement d'un signal delivre par un detecteur de rayonnement
US8954300B2 (en) 2008-03-31 2015-02-10 Southern Innovation International Pty Ltd. Screening method and apparatus
EP3062125A1 (fr) * 2015-02-26 2016-08-31 Fei Company Traitement d'impulsion
US10310099B2 (en) 2004-09-16 2019-06-04 Southern Innovation International Pty Ltd Method and apparatus for resolving individual signals in detector output data

Families Citing this family (48)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2870603B1 (fr) * 2004-05-19 2006-07-28 Commissariat Energie Atomique Mesure et traitement d'un signal comprenant des empilements d'impulsions elementaires
ITPI20040078A1 (it) * 2004-10-18 2005-01-18 I S E Ingegneria Dei Sistemi E Metodo ed apparecchiatura per il trattamento dei segnali generati da tubi fotomoltiplicatori
US20060212243A1 (en) * 2005-03-17 2006-09-21 Levine Frank E Event tracing using hash tables with support for dynamic address to name resolution
US7346476B2 (en) * 2005-03-17 2008-03-18 International Business Machines Corporation Event tracing with time stamp compression
US7369954B2 (en) * 2005-03-17 2008-05-06 International Business Machines Corporation Event tracing with time stamp compression and history buffer based compression
US7496902B2 (en) * 2005-03-17 2009-02-24 International Business Machines Corporation Data and instruction address compression
US7439515B2 (en) * 2005-06-17 2008-10-21 Siemens Medical Solutions Usa, Inc. Pipeline processing of pulse pile-up correction in a nuclear medicine imaging system
US7688944B2 (en) 2005-07-01 2010-03-30 Mayo Foundation For Medical Education And Research System and method for time-of-flight imaging
JP2009501934A (ja) * 2005-07-19 2009-01-22 ミツビシ・エレクトリック・リサーチ・ラボラトリーズ・インコーポレイテッド 受信無線信号において立ち上がりエッジ期間を識別する方法及び受信機
CN101238392B (zh) 2005-08-04 2012-03-14 皇家飞利浦电子股份有限公司 用于pet的模块化信号处理主链
US7211800B2 (en) * 2005-09-29 2007-05-01 Siemens Medical Solutions Usa, Inc. Afterglow DC-offset calibration in a nuclear imaging system
US7208739B1 (en) * 2005-11-30 2007-04-24 General Electric Company Method and apparatus for correction of pileup and charge sharing in x-ray images with energy resolution
US8247781B2 (en) 2005-12-01 2012-08-21 Innovative American Technology, Inc. Fabrication of a high performance neutron detector with near zero gamma cross talk
US20100226580A1 (en) * 2005-12-01 2010-09-09 Innovative American Technology Inc. System and method for increased gamma/neutron detection
WO2007146350A2 (fr) * 2006-06-14 2007-12-21 Baker Hughes Incorporated Rejet d'empilement
US20080075342A1 (en) * 2006-09-27 2008-03-27 Lazuka David M Pet scanner with digital trigger
CN101542316B (zh) * 2006-11-30 2013-03-27 皇家飞利浦电子股份有限公司 利用相关的光子数和能量测量的谱计算机断层摄影
ATE510231T1 (de) * 2006-12-13 2011-06-15 Koninkl Philips Electronics Nv Gerät und verfahren zur zählung von röntgenphotonen
EP2156218A2 (fr) * 2007-06-01 2010-02-24 Koninklijke Philips Electronics N.V. Détecteur de comptage de photon spectral
WO2008155680A2 (fr) * 2007-06-19 2008-12-24 Koninklijke Philips Electronics N.V. Détecteur de comptage de photons spectral
DE112008001646T5 (de) * 2007-06-20 2010-06-10 Thermo Electron Scientific Instruments LLC, Madison Bearbeitung von Spektrometer-Pile-Up-Ereignissen
EP2179522B1 (fr) * 2007-08-03 2018-08-29 Judith B. Mott Revocable Trust Dated June 6, 2006, As Amended And Restated Correction de pente de processeur d'impulsions numériques
US7855370B2 (en) * 2007-08-03 2010-12-21 Pulsetor, Llc Pileup rejection in an energy-dispersive radiation spectrometry system
US7741609B2 (en) * 2007-08-03 2010-06-22 Pulsetor, Llc Adapting a high-performance pulse processor to an existing spectrometry system
US8340377B2 (en) * 2007-09-17 2012-12-25 Siemens Medical Solutions Usa, Inc. Method for energy calculation and pileup determination for continuously sampled nuclear pulse processing
US7807973B2 (en) * 2008-08-01 2010-10-05 Pulsetor, Llc Pileup rejection in an energy-dispersive radiation spectrometry system
US8410451B2 (en) 2009-04-09 2013-04-02 Boss Physical Sciences Llc Neutron fluorescence with synchronized gamma detector
US8785864B2 (en) 2009-09-22 2014-07-22 Boss Physical Sciences Llc Organic-scintillator compton gamma ray telescope
US8481947B2 (en) * 2009-09-29 2013-07-09 Tilahun Woldeselassie Woldemichael Method and system for nuclear imaging using multi-zone detector architecture
US9279888B2 (en) * 2009-10-01 2016-03-08 Kabushiki Kaisha Toshiba System for online/offline singles-pairing with keeping/rejecting multi-coincidences for positron emission tomography
US8618495B2 (en) 2010-05-03 2013-12-31 Brookhaven Science Associates, Llc Method and apparatus for analog pulse pile-up rejection
RU2467353C1 (ru) * 2011-03-31 2012-11-20 Федеральное государственное унитарное предприятие "Всероссийский научно-исследовательский институт автоматики им. Н.Л. Духова" (ФГУП "ВНИИА") Способ определения порога обнаружения радиационного монитора
EP2543813A1 (fr) * 2011-07-08 2013-01-09 Nederlandse Organisatie voor toegepast -natuurwetenschappelijk onderzoek TNO Système de télémétrie, tuyau et procédé de transmission d'informations
CN104024886B (zh) 2011-12-21 2017-12-26 皇家飞利浦有限公司 用于考虑堆积事件来探测光子的探测装置
RU2524439C1 (ru) * 2013-03-20 2014-07-27 Федеральное государственное унитарное предприятие "Всероссийский научно-исследовательский институт автоматики им. Н.Л. Духова" (ФГУП "ВНИИА") Способ определения порога обнаружения радиационного монитора
US9128194B2 (en) * 2013-04-19 2015-09-08 Kabushiki Kaisha Toshiba Pileup correction method for a photon-counting detector
JP6411044B2 (ja) * 2014-03-20 2018-10-24 株式会社東芝 信号処理装置、放射線検出装置および信号処理方法
US9851457B2 (en) 2014-09-02 2017-12-26 Bridgeport Instruments, Llc Compensating for pulse shape variation of light in scintillators
US9606245B1 (en) 2015-03-24 2017-03-28 The Research Foundation For The State University Of New York Autonomous gamma, X-ray, and particle detector
US9869791B2 (en) 2015-06-17 2018-01-16 Baker Hughes, A Ge Company, Llc Measurement of downhole radiation
US9696439B2 (en) 2015-08-10 2017-07-04 Shanghai United Imaging Healthcare Co., Ltd. Apparatus and method for PET detector
WO2018002744A1 (fr) * 2016-06-29 2018-01-04 Siemens Medical Solutions Usa, Inc. Système et procédé pour désempiler des impulsions se chevauchant
US10162066B2 (en) 2017-02-06 2018-12-25 General Electric Company Coincidence-enabling photon-counting detector
US9945963B1 (en) * 2017-08-01 2018-04-17 Siemens Medical Solutions Usa, Inc. Dynamic control of event dumping
CN109816740B (zh) * 2017-11-18 2020-10-16 苏州瑞派宁科技有限公司 一种闪烁脉冲事件的符合处理方法
US10353087B1 (en) * 2018-04-17 2019-07-16 Siemens Medical Solutions Usa, Inc. Coincidence circuit with splitter
US11774628B2 (en) 2019-05-24 2023-10-03 Halliburton Energy Services, Inc. Probabilistically distinguishing between true and false scintillator pulses
CN112587161B (zh) * 2020-12-09 2022-09-30 明峰医疗系统股份有限公司 堆积信号恢复方法、pet成像设备及计算机可读存储介质

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5430406A (en) * 1989-12-22 1995-07-04 Adac Laboratories, Inc. Method and apparatus for measurement of time integrals of exponentially decaying pulses
US5532944A (en) * 1994-07-28 1996-07-02 Sorrento Electronics, Inc. Multi-channel analysis system and method using digital signal processing

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3747001A (en) * 1972-02-17 1973-07-17 Atomic Energy Commission Pulse processing system
US4455616A (en) * 1979-07-09 1984-06-19 Elscint, Ltd. Fast gamma camera
DE3584477D1 (de) * 1984-06-30 1991-11-28 Shimadzu Corp Halbleiterstrahlungsdetektor.
US4999501A (en) * 1985-08-27 1991-03-12 Baylor College Of Medicine High speed multiwire photon camera
US5319204A (en) * 1992-05-13 1994-06-07 Board Of Regents, The University Of Texas System Positron emission tomography camera with quadrant-sharing photomultipliers and cross-coupled scintillating crystals
US5453623A (en) * 1992-05-13 1995-09-26 Board Of Regents, The University Of Texas System Positron emission tomography camera with quadrant-sharing photomultipliers and cross-coupled scintillating crystals
US5349193A (en) * 1993-05-20 1994-09-20 Princeton Gamma Tech, Inc. Highly sensitive nuclear spectrometer apparatus and method
PT1007988E (pt) * 1997-05-07 2003-12-31 Univ Texas Processo e aparelho para evitar a acumulacao quando da deteccao da energia de sinais de entrada
WO2000073819A1 (fr) * 1999-05-27 2000-12-07 Analyser Systems Ag Procede et appareil permettant le rejet d'empilages d'impulsions numeriques selon des parametres mutliples

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5430406A (en) * 1989-12-22 1995-07-04 Adac Laboratories, Inc. Method and apparatus for measurement of time integrals of exponentially decaying pulses
US5532944A (en) * 1994-07-28 1996-07-02 Sorrento Electronics, Inc. Multi-channel analysis system and method using digital signal processing

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10310099B2 (en) 2004-09-16 2019-06-04 Southern Innovation International Pty Ltd Method and apparatus for resolving individual signals in detector output data
US8618471B2 (en) 2006-10-25 2013-12-31 Koninklijke Philips N.V. Apparatus, imaging device and method for detecting X-ray radiation
WO2008050283A3 (fr) * 2006-10-25 2008-07-10 Koninkl Philips Electronics Nv Appareil, dispositif d'imagerie et procédé pour détecter un rayonnement de rayons x
US8954300B2 (en) 2008-03-31 2015-02-10 Southern Innovation International Pty Ltd. Screening method and apparatus
US8471210B2 (en) 2008-03-31 2013-06-25 Southern Innovation International Pty Ltd. Radiation imaging method with individual signal resolution
AU2009230875B2 (en) * 2008-03-31 2014-07-10 Southern Innovation International Pty Ltd Method and apparatus for borehole logging
WO2009121131A1 (fr) * 2008-03-31 2009-10-08 Southern Innovation International Pty Ltd Procédé et appareil de diagraphie de forage
US9310513B2 (en) 2008-03-31 2016-04-12 Southern Innovation International Pty Ltd. Method and apparatus for borehole logging
US8812268B2 (en) 2008-12-18 2014-08-19 Southern Innovation International Pty. Ltd. Method and apparatus for resolving piled-up pulses by using a mathematical transform
EP2461183A3 (fr) * 2010-10-19 2014-05-21 Kabushiki Kaisha Toshiba Module détecteur de tomographie à émission de positrons, détecteur de radiations, système de balayage de tomographie à émission de positrons, procédé de traitement de signaux et procédé pour la fabrication du module détecteur de radiations
JP2012088306A (ja) * 2010-10-19 2012-05-10 Toshiba Corp Ｐｅｔ検出器モジュール、放射線検出器、ｐｅｔスキャナシステム、信号処理方法、及び放射線検出器モジュールの製造方法
EP3399342A1 (fr) * 2010-10-19 2018-11-07 Toshiba Medical Systems Corporation Module détecteur de tomographie à émission de positrons, détecteur de radiations, système de balayage de tomographie à émission de positrons, procédé de traitement de signaux et procédé pour la fabrication du module détecteur de radiations
WO2012101332A1 (fr) * 2011-01-27 2012-08-02 Michel Tararine Procede et dispositif de correction d'empilement d'impulsions pour un detecteur de rayonnement
US9464996B2 (en) 2011-07-26 2016-10-11 Multix Sa Processing device and method for the spectrometric measurement of a photon flux
FR2978562A1 (fr) * 2011-07-26 2013-02-01 Multix Sa Dispositif et procede de traitement pour une mesure spectrometrique d'un flux de photons
WO2013014132A1 (fr) * 2011-07-26 2013-01-31 Multix Sa Dispositif et procede de traitement pour une mesure spectrometrique d'un flux de photons
US9696432B2 (en) 2013-02-28 2017-07-04 Commissariat à l'énergie atomique et aux énergies alternatives Device for processing a signal delivered by a radiation detector
WO2014132003A1 (fr) * 2013-02-28 2014-09-04 Commissariat A L'energie Atomique Et Aux Energies Alternatives Dispositif de traitement d'un signal delivre par un detecteur de rayonnement
EP2962129B1 (fr) * 2013-02-28 2020-03-18 Commissariat à l'Energie Atomique et aux Energies Alternatives Dispositif de traitement d'un signal delivre par un detecteur de rayonnement
CN105929436A (zh) * 2015-02-26 2016-09-07 Fei 公司 脉冲处理
US20160254119A1 (en) * 2015-02-26 2016-09-01 Fei Company Pulse processing
EP3062126A1 (fr) 2015-02-26 2016-08-31 FEI Company Traitement d'impulsion
EP3062125A1 (fr) * 2015-02-26 2016-08-31 Fei Company Traitement d'impulsion
US10403470B2 (en) * 2015-02-26 2019-09-03 Fei Company Pulse processing
CN105929436B (zh) * 2015-02-26 2020-06-09 Fei 公司 脉冲处理

Also Published As

Publication number Publication date
EP1444534A2 (fr) 2004-08-11
US6936822B2 (en) 2005-08-30
CA2463756A1 (fr) 2003-05-15
WO2003040757A3 (fr) 2003-11-27
US20040036025A1 (en) 2004-02-26

Similar Documents

Publication Publication Date Title
US6936822B2 (en) Method and apparatus to prevent signal pile-up
EP1007988B1 (fr) Procede et appareil destines a empecher l'empilement lors de la detection de l'energie de signaux entrants
JP6657398B2 (ja) パルスパイルアップイベントのリアルタイム処理の方法及びシステム
US9354351B2 (en) High throughput pulse height analyzer
US8859951B2 (en) Method and apparatus for photosensor gain and scintillation crystal optical coupling monitoring in radiation detectors
US6590215B2 (en) Readout circuit for a charge detector
JP2011519415A (ja) 個別信号解像度を用いた放射線画像形成法
Wong et al. A scintillation detector signal processing technique with active pileup prevention for extending scintillation count rates
EP0125403B1 (fr) Circuit pour le traitement d'impulsions utilisant la technique de saisie pondérée
Del Guerra et al. Use of a YAP: Ce matrix coupled to a position-sensitive photomultiplier for high resolution positron emission tomography
Li et al. A new pileup-prevention front-end electronic design for high resolution PET and gamma camera
Wong et al. A high count rate position decoding and energy measuring method for nuclear cameras using Anger logic detectors
Tan et al. A fast digital filter algorithm for gamma-ray spectroscopy of double-exponential decaying scintillators
CN106821409A (zh) 堆积事件处理方法及装置
Mohammadian-Behbahani Non-iterative pulse tail extrapolation algorithms for correcting nuclear pulse pile-up
Murphy et al. Clinical significance of scintillation camera electronics capable of high processing rates
US10866329B2 (en) System and method to unpile overlapping pulses
Tanaka et al. A new method for preventing pulse pileup in scintillation detectors
Xie et al. A new approach for pulse processing in PET
US10330797B2 (en) Method for dead time determination in a gamma camera and a system for accomplishing the same
Woldemichael Modeling of scintillation cameras with multi-zone architecture and pileup prevention circuitry
Wells et al. Count rate performance and deadtime analysis of the new 3D PETRRA PET camera
Han et al. A VLSI design for energy extraction and pileup prevention for high count-rate scintillation signals
Daniel Gamma decay of Rhenium 186
Douglas et al. Investigating the impact of LSO on the count rate of wholebody PET tomographs

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A2

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EC EE ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NO NZ OM PH PL PT RO RU SD SE SG SI SK SL TJ TM TN TR TT TZ UA UG US UZ VN YU ZA ZM ZW

AL Designated countries for regional patents

Kind code of ref document: A2

Designated state(s): GH GM KE LS MW MZ SD SL SZ TZ UG ZM ZW AM AZ BY KG KZ MD RU TJ TM AT BE BG CH CY CZ DE DK EE ES FI FR GB GR IE IT LU MC NL PT SE SK TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
WWE Wipo information: entry into national phase

Ref document number: 2463756

Country of ref document: CA

WWE Wipo information: entry into national phase

Ref document number: 2002799158

Country of ref document: EP

WWP Wipo information: published in national office

Ref document number: 2002799158

Country of ref document: EP

NENP Non-entry into the national phase

Ref country code: JP

WWW Wipo information: withdrawn in national office

Country of ref document: JP

WWW Wipo information: withdrawn in national office

Ref document number: 2002799158

Country of ref document: EP